Numerous epidemiological studies have shown the adverse effects of traffic-related air pollution (TRAP) exposure on asthma and related inflammatory phenotypes in children and adults. Although genome-wide association studies (GWAS) have identified variants associated with asthma, there has been limited success in identifying genes that modulate susceptibility to TRAP exposure. We propose an innovative genetics approach in mice and humans to identify novel variants that interact with TRAP to affect immunoregulatory endophenotypes and risk of childhood asthma. Specific Aim 1 will determine the immunoregulatory responses of ~150 mouse strains from the Hybrid Mouse Diversity Panel (HMDP) to diesel exhaust particles (DEP), a model traffic-related pollutant. Mice will undergo a 2-week intranasal exposure protocol after which cellular immunoregulatory phenotypes will be determined in lung and spleen. The relationship between these traits to lung function will also be assessed. We will use these data to carry out a gene-environment (GxE) GWAS to identify loci that influence immunoregulation through interactions with DEP exposure. In preliminary studies with ~40 HMDP strains, we observed ~10-fold variability in immunoregulatory endophenotypes and identified 2 loci on chromosomes 4 and 16 that exhibited highly suggestive association with pulmonary Treg frequency. Notably, previous GWAS have identified the corresponding loci on human chromosomes 1 and 3, respectively, as being associated with childhood asthma-related phenotypes. These preliminary findings are consistent with our hypothesis that genetic background modulates the response to TRAP and support the use of our proposed integrative genetics approach to identify novel asthma susceptibility loci. In Specific Aim 2, we will use synteny mapping to identify loci that affect asthma-related phenotypes in children through GxE interactions. This will be accomplished by leveraging already existing genetic, exposure, and clinical data in 4 large cohorts. First, we will use GWAS results from the Children's Health Study (CHS) to determine whether regions of the human genome that are syntenic to those identified the HMDP interact with TRAP exposure to affect asthma-related traits. Loci exhibiting GxE interactions will be replicated in the Genetics o Asthma in Latino Americans (GALA) 1 & II and Study of African Americans, Asthma, Genes, & Environments (SAGE) II cohorts. For loci exhibiting consistent GxE interactions, we will leverage already existing biological samples in these cohorts to investigate methylation at the FoxP3 promoter and FoxP3 mRNA levels, as surrogate measures of Treg function/frequency. Importantly, the clinical phenotypes and estimates of TRAP exposure are highly comparable in these 4 cohorts, thus increasing the likelihood of identifying and validating true GxE loci. The integrative genomics approaches proposed herein could lead to a better understanding of the interrelationships between genes, environmental exposures, immunoregulatory endophenotypes, and asthma, which could have important clinical, epidemiological, and translational implications for developing novel treatment strategies.